1. Field of the Invention
The object of the present invention relates to a process for the determination of speed limits on a road used by a motor vehicle and a process for the operation of this system. The aim of the present invention is essentially to propose a solution whereby, under all conditions, information relating to a speed limitation to be applied to a road in use, or on the point of being used, by a motor vehicle. The information collected in this manner can then be used in the different applications with which the vehicle in question is equipped. Notably, but not in a limiting manner, information relating to a speed limitation can be used within a system aimed at helping to indicate explicitly the maximum authorized speed limit to the driver if the latter has exceeded this limit.
2. Description of the Related Art
In a general manner, the purpose of the invention is to assist driving by proposing a series of systems aimed at assisting the driver and essentially intended to improve road safety conditions. In this way, for example, the following developments have been made:
systems described as night vision systems to help the driver to detect in advance objects, which would otherwise be difficult to detect under night time driving conditions;
systems designed for the advance anticipation of bends, with the aim of warning the driver at an early stage of an approaching bend.
Within the framework of systems intended to aid driving, there have also been attempts to propose systems for warning drivers of speed limitations. A system of this nature must enable a speed limit on a road that is in use, or a road that is to be in use, to be automatically detected by a vehicle. In fact, action relating to excessive speeds is necessary in order to reduce the number of accidents and the gravity of their consequences. Many drivers do not respect the speed regulations: 40% of them do not respect the motorway speed limits, 60% do not respect speed limits on national and departmental and 25% of drivers exceed urban speed limits by more than 10 km/h.
To date, there have been two sorts of proposals for the automatic determination of a speed limit applicable to a particular road.
The first type of solution lies in the manner in which information coming from a navigation system is used. Such navigation systems are increasingly installed in vehicles in order to guide the driver from one point (corresponding to the actual position of his vehicle) to a destination point (chosen by the driver). They combine map information with information relating to the position of the vehicle provided by a GPS system and often enable to know in advance the characteristics of the road. Furthermore, information connected with the characteristics of the road is linked to the speed limitation associated with this road. Other information, typically indications of road junctions or motorway exits, for example, are also available using this system. Moreover, if the driver chooses a route from point A to point B, the route that the vehicle is likely to take is known in advance and the knowledge of the speed limitations that are likely to be in force in this route can, on the whole, be anticipated up to a distance of ten kilometers beforehand.
Nevertheless, the system comprises a number of inherent weaknesses that limit its effectiveness:
current cartography is still very imprecise. It frequently happens that information is completely lacking at a given place. In fact, there may be entire areas throughout the world that are not completely covered by the cartographical data bases;
it can also happen that the information supplied by the navigation system is incorrect. For example, if a driver intends heading for a place B that he has stored in his navigation system and if, finally, during his journey he is obliged to head for a place C without following the instructions given by his navigation system, the instructions given by this system are confusing or even contradictory in relation to the characteristics of the route that the vehicle is actually following;
variations in the configuration of the road as a result of unexpected events, for example, road works, can have the effect of modifying the speed limit over the part of the road in question; these modifications are not known to the navigation system.
it is also possible for GPS cover to be lost completely for a time, for example, when driving through a long tunnel.
There is a second type of solution for automatically determining a speed limit that is in force based on using information supplied by an image processing system. This type of system makes use of at least one camera and image processing software applications. The camera captures images along the road and the image processing system indicates any speed limit panels and enables the symbols on these panels to be read. This system then displays the speed limit panel that has been detected with a certain degree of accuracy. One such known system is the “Speed Limit Support” system, which helps drivers by informing them of the speed limits on the road on which they are driving, so as to ensure that these limits are not exceeded. This system is intended to complement the manual speed limiter, which is already commercially available in certain vehicles.
However, such systems are likely to be unreliable in certain traffic situations, especially at motorway exit points, during the night or if a vehicle is travelling at high speed and more particularly, where different speed limits apply for different types of vehicles. In these cases, the correct functioning of the algorithms for the recognition of the different characters on the speed restriction panels cannot be guaranteed. Moreover, at junctions, bifurcations or where there are several traffic lanes, systems of this type are unable to detect the relevant speed restriction panels, as there can be different panels in force for different traffic lanes, and they are unable to distinguish effectively between these panels and road in question. In addition, it has to be observed that the range of such systems is usually no more than a few dozen meters, with the result that they are unable to detect the panels if they are obscured by obstacles in front of the vehicle or by a succession of bends.
Consequently, none of the existing systems are entirely satisfactory for the automatic detection of current speed limits on a busy road.